1. Field of the Invention
The present invention relates to a light source device used for normal observation using normal light and fluorescence observation using fluorescence and an endoscope apparatus using the light source device.
2. Description of the Related Art
Examples of observation of living tissue using an endoscope include fluorescence observation, which applies excitation light and performs observation using a fluorescence image, in addition to normal endoscopic observation using visible light (normal light). The fluorescence observation takes advantage of the fact that when light with a wavelength of 400 to 480 nm (excitation light) is applied to living tissue, a normal tissue emits strong fluorescence with a wavelength in the range of about 480 to 630 nm while a diseased part such as a cancerous cell emits weak fluorescence and is known as a technique capable of detecting an abnormal part such as early cancer which is hard to visually recognize by normal endoscopic observation.
A conventional endoscope apparatus for fluorescence observation generates excitation light necessary for fluorescence observation by an excitation light filter which is arranged in an optical path of illumination light emitted from a light source and transmits only excitation light. The endoscope apparatus applies excitation light to living tissue and obtains autofluorescence by a fluorescence transmission filter which is arranged between an objective optical system at a distal end portion of an insertion portion of an endoscope and a solid-state image pickup device and transmits only light with a fluorescence wavelength.
In recent years, endoscope apparatuses capable of normal observation using normal light and fluorescence observation using fluorescence have been proposed. For example, some of the endoscope apparatuses generate, from light from a light source, excitation light through an excitation light filter provided on a rotating filter, apply the excitation light to living tissue, and obtain fluorescence.
For example, Japanese Patent Application Laid-Open Publication No. 2002-336196 discloses a technique related to an endoscope apparatus configured to be capable of switching between a normal image mode and a fluorescence image mode by arranging a switching filter which is a rotating plate in an optical path from a light source and concentrically providing an RGB filter for normal observation and a fluorescence observation filter on an inner peripheral side and an outer peripheral side of the switching filter.
Japanese Patent Application Laid-Open Publication No. 2007-175210 discloses a technique related to an endoscope apparatus which has a lamp and an excitation light unit within a light source device and is configured such that a dichroic mirror for combining optical paths for the lamp and excitation light unit is arranged between a rotating plate and a condensing lens.
Japanese Patent Application Laid-Open Publication No. 2007-143647 discloses a technique related to an endoscope apparatus configured for fluorescence observation to compensate for a deficiency in the amount of excitation light by lighting an excitation light light-emitting device (blue LED) to suit excitation light emitted when white light is filtered through a rotating filter.